Lithographic duplicating method and lithoplate master therefor

ABSTRACT

A high quality long run lithographic-printing plate is produced by applying an alpha-naphthol first reactant at image areas to a lithoplate master containing an ionic iodide coreactant, most particularly a quaternary ammonium iodide coreactant, and heating the plate.

United States Patent- I l l 1 Inventors Appl. No.

Theodore A. Haas Maplewood:

Collin 11. Alexander, Falcon Heights, Minn. 773,358

Sept. 19, 1968 A Feb. 2, 1971 Minnesota Mining and Manufacturing CompanySt. Paul, Minn.

a corporation of Delaware LlTHOGRAPl-IIC DUPLICATING METHOD ANDLITHOPLATE MASTER THEREFOR 12 Claims, No Drawings US. Cl 101/467; 7101/462, 101/450; 250/65 Int. Cl 841m 5/00, B41n 3/00 [50] Field ofSearch 101/450,

[ 56] References Cited UNITED STATES PATENTS 3,094,417 6/1963 Workmanl01/467UX 3,094,619 6/1963 Grant 250/65( 1) 3,168,864 2/1965 Brandl etal. 101/467 3,299,807 1/1967 Evensen 101/467 Primary ExaminerDavid KleinAttorney-Kinney, Alexander, Sell, Steldt & Delahunt coreactant, andheating the plate.

LITHOGRAPHIC DUPLICATING METHOD AND LITHOPLATE MASTER THEREFOR Thisinvention relates to the art of duplicating and more particularly tomaterials and methods useful in the planographic or lithographicprinting art.

The duplicating of graphic matter by lithography normally involves theereationon a preferentially hydrophilic surface of preferentiallyoleophilic ink receptive image areas corresponding to the image-definingareas of the original. An oily ink is selectively taken up by the imageareas while the nonimage areas are maintained in a water wet and inkrepellent state. The ink is then transferred under pressure, eitherdirectly or by way of an intermediate transfer surface, to the surfaceof the paper or other print sheet.

Various methods have been devised for forming the ink receptive image. Awaxy image may be imparted to a water receptive surface, e.g. with waxcrayons, or by heat-, impact-, or pressure-induced transfer from awax-coated carbon paper or other transfer sheet. Water-soluble orhydrophilic light-sensitive coatings, e.g. of dichromated colloid or ofdiazo resin, may be rendered ink receptive on exposure to a light image.Oily or waxy or polymeric ink receptive inclusions within a hydrophiliccoating may be made available at the surface by localized application ofpressure or heat.

Transfer of reactant materials from an exposed light sensitiveintermediate sheet to a receptor sheet containing an image formingcoreactant has previously been suggested, e.g. in U.S. Pat. Nos.3,094,417 and 3,094,619. Under reflex exposure the first reactant ismade nonreactive above the reflective background areas but a smallportion of the reactant lying above the light absorptive image areas ofthe original remains unchanged. Heating the exposed intermediate againsta receptor sheet then causes reaction with the coreactant and formationof a corresponding image on the receptor. This procedure, along withothers, is suggested in German'Pat. No. 1,263,032, as a method offorming oleophilic image areas on a lithographic plate containing areducible metal salt such as cupric nitrate or ferric sulfate ascoreactant, the metal salt being reduced to an oleophilic imagingmaterial.

The present invention likewise involves the imaging with a firstreactant of a sheet material containing a coreactant, but differs fromthe prior art in a number of significant respects, most particularly inthe material employed as coreactant. The first reactant is analpha-naphthol as defined in U.S. Pat. No. 3,094,619, having directlyattached to the'hydroxy-substituted aromatic ring a preponderance ofelectron donor groups, as represented particularly by4-methoxy-lnaphthol. These normally reactive compounds are desensitizedby exposure to ultraviolet radiation or, in the presence of a sensitizersuch as erythrosin, by exposure to visible light, and are thereforeparticularly useful in the reproduction of printed or other graphicoriginals.

The lithographic plates employed in making these lithomasters mayinclude silicated aluminum or other preferentially hydrophilic treatedmetal plates, but preferably comprise a dimensionally stable supportcoated with a preferentially hydrophilic composition, e.g. containingclay or other hydrophilic mineral powder filler in a cross-linked orotherwise insolubilized polyvinyl alcohol or other water-insolublehydrophilic binder. Plasticizers, humectants, coloring materials, andother adjuvants or modifiers may be included as desired. Additionallythere is present an ionic iodide coreactant for the alpha-naphthol. Theinorganic iodides such as sodium or potassium iodide are effective, butthe organic ionic iodides generally, and in particular the quaternaryammonium iodides, are particularly advantageous. Compounds of the lattertype are found in particular to be highly resistant to migration withinthe hydrophilic coating under storage at high humidities. Typical ionicorganic iodide coreactants exhibiting high resistance to migrationinclude methyl triethyl ammonium iodide, propyl tributyl ammoniumiodide, ethyl triethanol ammonium iodide, phenyl trimethyl ammoniumiodide, methyl tris-(2-nitriloethanol) ammonium iodide,l-ethyl-quinaldinium iodide. l-methyl-quinolinium iodide.l-cthylpyridinium iodide. trimethyl sulfonium iodide. trimethylsulfoxonium iodide.

Nonionic iodides or iodine compounds. such for example iodoform. carbontctraiodide. phenyl iodide. or butyl iodide. are ineffective aseoreactants for the a-naphthols in the practice of this invention. asmay be determined by means of the following simple test procedure.

A stock solution of 4-methoxy-l-naphthol in equal parts of acetone andwater is first prepared. For this purpose the pure compound isineffective; but material which has undergone moderate exposure to lightor contact with the air. is fully ef fective. Accordingly. unlessextreme precautions have been taken to assure the use of the purecompound, a solution prepared under normal laboratory conditions andprocedures will be found to meet all requirements of the test. To asmall portion of the solution thus prepared is then added a small amountof an aqueous solution of the compound under test. The rapid formationof a deep blue coloration indicates that the compound will be useful asa coreactant. Reactant concentrations and amounts are so selected as topermit recognition of the color change. The nonionic compounds fail tocause the indicated color formation, whereas the blue color is quicklyobtained with the ionic iodides.

The coreactant must be present at or near the surface of the hydrophiliccoating to insure prompt and efficient reaction with reactantstransferred thereto. Thus the material may be incorporated within thecomposition prior to coating, but is more efficiently supplied as asubsequent top-coating applied over the previously coated, dried andinsolubilized hydrophilic material. Simple swabbing of the plate surfacewith a dilute aqueous solution of the coreactant. using a saturatedcotton pledget. is fully effective although usually productive of unevenor incomplete coatings. Use of a coating roller, air knife, or othermechanical device permits more accurate application. The coreactant mayalternatively be added to the hydrophilic coating composition prior toapplying the same to the supporting backing. As little as .025 gm./sq.m.of coreactant has been found adequate when carefully applied as a surface coating, although commercial coating practice usually requiressomewhat larger amounts. for example of .4 gm./sq.m. to insure completecoverage. On the other hand, good results have been obtained with asmuch as 2.5 gm./sq.m. of coreactant when introduced into the hydrophiliccoating composition. Much larger amounts of these water-solublematerials tend to reduce the anchorage of the oleophilic image and thusto shorten the press life of the plate.

The combination of photoreducible dye and 4-methoxy-lnaphthol orequivalent substituted a-naphthol as described in U.S. Pat. No.3,094,417 provides an intermediate sheet which under reflex exposure tovisible light is easily desensitized at background areas. Heating thethus exposed intermediate in face-to-face contact with a lithographicmaster prepared as above-described results in the formation at the platesurface of a faint blue image which is preferentially oleophilic and inkreceptive, and which is surprisingly resistant to removal. Lithoplatesimaged in the manner described have delivered many thousands ofexcellent copies without any discernible reduction in image quality ordensity.

In the following illustrative Examples all proportions are given inparts by weight unless otherwise indicated.

EXAMPLE 1 A commercial light sensitive intermediate sheet as describedin U.S. Pat. No. 3,094,417 and containing erythrosin and4-methoxy-l-naphthol in a polymeric binder on a thin transparent backingis placed against a printed original which is then exposed through theintermediate to uniform illumination from an incandescent tungstenfilament source. Exposure is just suffieient to cause complete desensitization at the areas contacting the reflective unprinted backgroundareas.

The intermediate is then placed in face-to-face contact with alithoplate master having a preferentially hydrophilic surface coating ona heavy paper backing. The coated surface has been swabbed lightly witha dilute aqueous solution of potassium iodide. and dried. The compositeis heated for a few seconds on a smooth heating platen maintained atabout l20 C. On removal of the intermediate. the plate is found tocontain a faint blue image corresponding to the printed image of theoriginal.

The plate is wet out with acidic aqueous etch solution, placed on apress. and used in printing several thousand excellent copies.

EXAMPLE 2 A coating composition is prepared to the following formula:

Parts Polyvinyl alcohol 5 Kaolin 50 Glycerine 0. 5 Dirnethylolurea 1Potassium iodides 1. 5

. Butanol (anti-foam agent) 4 Water ea 150-200 The amount of water isjust sufficient to provide a smoothly coatable mixture. The compositionis coated on high wet strength 73 lb. lithobase paper at a coatingweight, after drying, of lbs/ream of 3000 sq.ft. The coating weight isnot critical but should be sufficient to provide complete coverage and asmooth surface while avoiding excessive curling of the sheet or crackingof the coating. The sheet is dried and the coating is insolubilized byheating for 1 hour at 60 C., to provide a lithoplate master.

An intermediate sheet is prepared by coating thin transparent mapoverlay tracing paper with a composition containmg:

Parts 4-methoxy-1-naphthol 10 Cellulose acetate butyrate 3 Diphenylphthalate 0. 3

in sufficient acetone to provide a coatable solution, and drying. Thedry coating weight is approximately 4.5 gm./sq.m.

The intermediate sheet is placed in face-to-face contact with thelithoplate master and a document having printed image areas on a thinonionskin paper is laid over the intermediate with the printed surfaceexposed. The three-sheet composite is passed through a Thermofaxinfrared-copying machine in the back print" position. A blue image isfon'ned on the lithoplate master. The plate is etched and run on thepress, with production of a large number of lithographic copies.

The same intermediate is useful in imaging one or more additional platesby the same procedure.

EXAMPLE 3 A lithoplate master is prepared by coating lithobase paperwith a composition containing:

Watersufficient for spreading.

The coated sheet is dried and heated as in Example 2. The dry coatingweight is 10 lbs. per ream of 3000 sq.ft.

The coated surface is further coated with an aqueous 3 percent solutionof tetraethylammonium iodide, at a coating weight after drying of0.4gm./sq.m.

An intermediate prepared as in Example 2 is imprinted on the uncoatedsurface with suitable indicia, applied with a typewriter and by handlettering, to provide differentially radiation absorptive image andbackground areas. The intermediate is placed against the Iithoplatemaster and the composite is passed through the Thermofax"infrared-copying machine in back-print position, formingblue image areason the plate surface. The plate is etched and run on the press,producing a large number ofcopies.

The master plates prepared under this Example remain fully effectiveafter storage in a humidity cabinet.

EXAMPLE 4 Carbon black is dispersed in a volatile liquid alcohol-ketonemixture to form a writing ink. To portions of such ink are added smallamounts of various naphthols. the concentration being in the range ofone-half to 4 percent. Using a felt tip pen, markings are made with theseveral inks on a lithoplate master prepared as described under Example3, and the plate is held for a few seconds against a platen heated to F.The plate is etched and run on the press. Each of the marks made withthe ink containing a naphthol produces good copy; the control mark, madewith ink containing no naphthol, does not reproduce. The specificnaphthols tested are:

4-methoxyl -naphthol 2-methyl-4-methoxyl -naphthol 4-ethoxyl -naphthol l,4-dihydroxynaphthalene l ,3-dihydroxynaphthalene 4-aminol -naphthol Weclaim:

1. Method of printing comprising: applying a ring-substituted a-naphtholfirst reactant at image-defining areas to a lithoplate master having apreferentially hydrophilic-printing layer containing at the surfacethereof a water-soluble ionic iodide coreactant, and heating at leastsaid areas, to provide on said master a preferentially oleophilicimage-defining pattern; and then printing from said master by thelithographicprinting process; said a-naphthol being furthercharacterized as having directly attached to the hydroxy-substitutedaromatic ring a preponderance of electron donor groups selected from theclass consisting of alkyl, aryl, alkoxy, aryloxy, hydroxy and aminogroups.

2. Method of claim 1 wherein said a-naphthol is applied by transfer froma uniformly coated source sheet held in face-toface contact with saidmaster.

3. Method of claim 2 wherein said source sheet is heated at least atimage-defining areas during transfer of said anaphthol.

4. Method of claim 3 wherein said source sheet is locally heated atimage-defining areas by exposure of a differentially radiationabsorptive imaged original to intense radiation.

5. Method of claim 3 wherein said source sheet is uniformly heatedduring transfer of said a-naphthol and wherein said anaphthol is presenton said source sheet only at image-defining areas.

6. Method of claim 5 including the step of preparing the source sheet byreflex exposure of a graphic original to actinic radiation appliedthrough said source sheet, said source sheet initially having a uniformcoating of a said a-naphthol which is desensitizable by said radiation.

11. A paper lithoplate master including a paper base and apreferentially hydrophilic coating comprising a hydrophilicwater-insoluble binder and a hydrophilic particulate filler andcontaining a water-soluble ionic iodide.

12. The lithoplate master of claim 11 wherein said iodide is at maximumconcentration adjacent the exposed surface of said coating.

2. Method of claim 1 wherein said Alpha -naphthol is applied by transferfrom a uniformly coated source sheet held in face-to-face contact withsaid master.
 3. Method of claim 2 wherein said source sheet is heated atleast at image-defining areas during transfer of said Alpha -naphthol.4. Method of claim 3 wherein said source sheet is locally heated atimage-defining areas by exposure of a differentially radiationabsorptive imaged original to intense radiation.
 5. Method of claim 3wherein said source sheet is uniformly heated during transfer of saidAlpha -naphthol and wherein said Alpha -naphthol is present on saidsource sheet only at image-defining areas.
 6. Method of claim 5including the step of preparing the source sheet by reflex exposure of agraphic original to actinic radiation applied through said source sheet,said source sheet initially having a uniform coating of a said Alpha-naphthol which is desensitizable by said radiation.
 7. A lithoplatemaster including a preferentially hydrophilic-printing layer containingat the surface thereof a water-soluble ionic iodide.
 8. Lithoplatemaster of claim 7 wherein said ionic iodide is an organic compound. 9.Lithoplate master of claim 8 wherein said compound is a quaternaryammonium iodide.
 10. Lithoplate master of claim 7 wherein saidcoreactant is present to the extent of about .025 to 2.5 gm./sq.m.
 11. Apaper lithoplate master including a paper base and a preferentiallyhydrophilic coating comprising a hydrophilic water-insoluble binder anda hydrophilic particulate filler and containing a water-soluble ioniciodide.
 12. The lithoplate master of claim 11 wherein said iodide is atmaximum concentration adjacent the exposed surface of said coating.